and from there I'm going to suggest some books that may or may not be considered "fantasy/sci-fi" because the fall into the realm of mythology.
Mary Stewart's Merlin series.
The Mabinogion (This may have to wait until they are in their teens)
Susan Cooper's The Dark is Rising
The Druid's Tune by O. R. Melling
A Children's Treasury of Mythology
Grimm's Fairy Tales
Aesop's Fables
Morgan Llywelyn has written some very good books based on Irish mythology. I especially liked Red Branch it sticks very close to the Ulster Cycle, Táin Bó Cúailnge and the story of Deirdre.

Norse mythology for children. I'm sure there are some books out there.



I would also suggest all "non-European" mythologies and especially Aboriginal/Oceanic mythologies considering though Mama/auntie is of European decent she has deep roots in NZ.

Soak them in mythology. Asian, European, Native American, African, Middle Eastern.

A lot of that stuff comes up in literature and on important occasions.

Hmmm....I could tell you a story about how my husband was studying for his AD test to get a graduate program and how there were many questions I had to help him with because while my parents encouraged reading of reading, especially reading certain classics, his were not.
Ummm I dropped out of high school in the tenth grade but I knew answers to Literature questions he didn't despite 4.0 and his collage education.